1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device, which is applicable to a power semiconductor device required to have high breakdown voltage.
2. Description of the Background Art
In junction terminations of high-breakdown-voltage semiconductor devices such as high-breakdown-voltage diodes, bipolar transistors, power MOSFETs and IGBTs, an electric field at an end of a depletion layer in the vicinity of a principal junction surface needs to be mitigated. In order to mitigate the electric field at the end of the depletion layer, there has been conventionally employed a field plate structure or a forming structure for a reduced surface field (hereinafter, referred to as RESURF).
For example, Japanese Patent Application Laid-Open No. 08-306937 discloses the technology of combining the field plate structure and the RESURF layer forming structure, to thereby improve device breakdown voltage.
In the structure shown in FIG. 3 of Japanese Patent Application Laid-Open No. 08-306937, a RESURF layer is formed in a surface of an n type semiconductor substrate. The RESURF layer is formed so as to be connected to an electrode layer (p type anode region), and is composed of p type impurities having lower concentration compared with the electrode layer. In addition, the RESURF layer is formed with a predetermined distance from a channel stopper layer formed in the surface of the semiconductor substrate. Further, the semiconductor device shown in FIG. 3 of Japanese Patent Application Laid-Open No. 08-306937 is provided with a conductive film (field plate electrode) on the RESURF layer via an insulating film.
In a case where the thickness of the insulating film under the field plate electrode is small, which is disclosed in Japanese Patent Application Laid-Open No. 08-306937, avalanche occurs in the vicinity of the end of the field plate electrode, leading to a decrease in device breakdown voltage. Accordingly, the insulating film under the field plate electrode needs to have a large thickness.
However, the thickness of the insulating film causes an increase in gap between the semiconductor substrate and the insulating film. The increase in gap causes, for example, unevenness in resist application during resist formation or a decrease in focus margin during photolithography.